Gain size and strength with training that targets the type II muscle fibers. Research shows that the best methods for growing these largest and fastest muscle fibers include training with maximal load contractions, lifting to failure, and heavy eccentrics.
A recent review on the effect of strength training methods on muscle fiber type and size highlights the following relevant points:
• There are two main muscle fiber types: Slow-twitch fibers (type I) that contract slowly and produce the least force. They have a high endurance capacity, particularly when trained aerobically. Fast-twitch (type II) fibers contract quickly and produce greater force. Within type II fibers there are both type IIX fibers that are the most powerful, largest fibers, and type IIA fibers that are smaller, slightly less powerful, but have much greater endurance capacity.
• Aerobic training not only increases the capacity of the slow type I fibers, it almost fully blunts the hypertrophic response from concurrent strength training.
• Strength training increases the percentage of type IIA fibers at the expense of type IIX fibers. Detraining—that is, stopping strength training for a period—has been shown to produce an increase in type IIX fibers at the expense of type IIA fibers.
• Researchers note that from a functional point of view the shift from type IIX to type IIA fibers with training may seem unfavorable since the IIX fibers are the fastest and most powerful. This is the case when analyzing individual fibers, however, the power capabilities of the whole intact muscle has proven to be greatest when the optimal strength training stimulus is performed, even though the end result is a shift to type IIA from IIX fibers.
• The type IIA fibers grow two times larger than type I fibers so that heavy strength training produces a relatively larger proportion of muscle cross-sectional area being made up of fast fibers. Simply, the type IIA fibers are so much larger than the type I fibers that this combination makes athletes faster and more powerful than if they did not train but had a greater proportion of type IIX fibers.
• Another factor is the ability to activate satellite cells—the “quiet” or dormant cells in the type II fibers. Satellite cells regulate the hypertrophy a trainee will experience. Typically, trainees can increase muscle size by 25 percent over baseline and will then hit a plateau unless the satellite cells are optimally trained. Do this by including maximal load lifts for 1 to 3 reps, training to failure on occasion, and doing eccentric enhanced training.
Maximal or near maximal load training (93 percent of the 1RM) has been shown to activate satellite cells and produce greater hypertrophy than training that combined ballistic training with near maximal load lifting.
Training to failure will activate satellite cells and recruit the highest threshold type II fibers to a greater degree than not training to failure but doing more volume.
Eccentric-enhanced training, either with super heavy eccentrics, or by modifying the tempo of the eccentric motion will increase satellite cells and type IIA fiber size and strength.
Andersen, J., and Aagaard, P. Effects of Strength Training on Muscle Fiber Types and Size: Consequences for Athletes Training for High-Intensity Sport. Scandinavian Journal of Medicine and Science in Sports 2010. 20(Suppl 2), 32-38.